A mixture In which the particles are to small to b seen with the naked eye is?

When the particles of a solution or a mixture are so small that they cannot be seen directly from our naked eyes the mixture was formed due called colloid. These are heterogeneous mixtures.

Explanation:

There are different methods to tell a mixture from compound and in this case it is done by passing light through it. When a beam of light is passed through this mixture the particles although being small all are enough such that scattering of the beam takes place and its path can be seen.